Network Programming in Python

import socket
host = 'www.google.com'
addr = socket.gethostbyname(host)
print(f"The ip address for {host} - ", addr)

import socket
mysock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
mysock.connect(('data.pr4e.org', 80))
cmd = 'GET http://data.pr4e.org/romeo.txt HTTP/1.0\r\n\r\n'.encode()
mysock.send(cmd)
while True:
    data = mysock.recv(512)
    if len(data) < 1:
        break
    print(data.decode(),end='')
mysock.close()

%%writefile serverprog.py
import socket
#SERVER NAME AND ADDRESS
host = 'localhost'
port = 5000
#CREATE SERVER SIDE SOCKET USING TCP
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
#BIND SOCKET WITH SERVER AND PORT
s.bind((host,port))
#ALLOW MAX ONE CONNECTION TO THE SOCKET
s.listen(1)
# WAIT TILL CLIENT ACCEPTS CONNECTION
c,addr = s.accept()
# DISPLAY CLIENT ADDRESS
print("connection established from - ", str(addr))
# SEND ENCODED MESSAGE TO CLIENT
c.send(b"Hello client, How are you?")
msg = 'bye'
c.send(msg.encode())
# DISCONNECT SERVER
c.close()

%%writefile clientprog.py
import socket
# TAKE SERVER NAME AND ADDRESS
host = 'localhost'
port = 5000
#CREATE CLIENT SIDE SOCKET USING TCP
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
#CONNECT SOCKET WITH SERVER AND PORT
s.connect((host,port))
# RECEIVE MAX 1024 BYTES MESSAGE FROM SERVER AT A TIME
msg = s.recv(1024)
# REPEAT AS LONG AS MESSAGE IS NOT EMPTY
while msg:
    print("Received - ", msg.decode())
    msg = s.recv(1024)
# DISCONNECT SERVER
s.close()

%%writefile udpserver.py
import socket
import time
#SERVER NAME AND ADDRESS
host = 'localhost'
port = 5000
#CREATE SERVER SIDE SOCKET USING TCP
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
# SERVER WAITS FOR 5 SECONDS 
time.sleep(5)
# SEND ENCODED MESSAGE TO CLIENT
s.sendto(b"Hello client, How are you?", (host,port))
msg = 'bye'
s.sendto(msg.encode(),(host,port))
# DISCONNECT SERVER
s.close()

%%writefile udpclient.py
import socket
# TAKE SERVER NAME AND ADDRESS
host = 'localhost'
port = 5000
#CREATE CLIENT SIDE SOCKET USING TCP
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
#CONNECT SOCKET WITH SERVER AND PORT
s.bind((host,port))
# RECEIVE MAX 1024 BYTES MESSAGE FROM SERVER AT A TIME
msg,addr = s.recvfrom(1024)
try :
    # SOCKET BLOCKS AFTER 5 SEC IF SERVER DISCONNECTS
    s.settimeout(5)
    # REPEAT AS LONG AS MSG IS NOT EMPTY
    while msg:
        print("Received - ", msg.decode())
        msg,addr = s.recvfrom(1024)
except socket.timeout:
    print("time is over and hence terminating")
# DISCONNECT SERVER
s.close()

%%writefile server2.py
import socket
#SERVER NAME AND ADDRESS
host = 'localhost'
port = 9000
#CREATE SERVER SIDE SOCKET USING TCP
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
#BIND SOCKET WITH SERVER AND PORT
s.bind((host,port))
#ALLOW MAX ONE CONNECTION TO THE SOCKET
s.listen(1)
# WAIT TILL CLIENT ACCEPTS CONNECTION
c,addr = s.accept()
# DISPLAY CLIENT ADDRESS
print("connection established from - ", str(addr))
# RUN SERVER CONTINUOUSLY
while True:
    data = c.recv(1024)
    #IF CLIENT SENDS EMPTY STRING, COME OUT OF WHILE LOOP
    if not data:
        break
    print("From client - " + str(data.decode()))
    # ENTER RESPONSE FROM SERVER
    data1 = input("Enter the response = ")
    # SEND THAT DATA TO CLIENT
    c.send(data1.encode())
# DISCONNECT SERVER
c.close()

%%writefile client2.py
import socket
# TAKE SERVER NAME AND ADDRESS
host = 'localhost'
port = 9000
#CREATE CLIENT SIDE SOCKET USING TCP
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
#CONNECT SOCKET WITH SERVER AND PORT
s.connect((host,port))
# ENTER DATA AT CLIENT 
str = input("Enter data - ")
# REPEAT AS LONG AS MESSAGE IS NOT exit
while str != 'exit':
   # SEND  DATA FROM CLIENT TO SERVER
    s.send(str.encode())
    # RECEIVE RESPONSE DATA FROM SERVER
    data = s.recv(1024)
    data = data.decode()
    print("From server - " + data)
    # ENTER DATA
    str = input("Enter data - ")
# DISCONNECT SERVER
s.close()

# importing the sockets module
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
target = input('What you want to scan?: ')
# getting the ip address using gethostbyname function
t_IP = socket.gethostbyname(target)
print("Starting scan on host: ", t_IP)
#create function port_scan
def port_scan(port):
    try:
        s.connect((t_IP, port))
        return True
    except:
        return False
#user input to ask for port number to be scanned
port = int(input("Enter the port number to be scanned: "))
if port_scan(port):
    print('Port', port, 'is open')
else:
    print("port", port, "is closed")